The Great White Dragon is rarely seen. Nobody knows where he slumbers, but they do know his cave is on one of the highest peaks in the world. Only few stories have made it to be Known about across the lands. Few ever made it back to there home villages to tell the story.
A shape-shifter of some sort has taken up a post at the War College of an enemy realm, where he secretly picks off only the most promising officer cadets, arranging bizarre accidents that gradually debase the leadership of the hostile army. In the long run, this will improve his nation's chances when the inevitable conflict comes.
As a shape-shifter he can impersonate superiors and peers alike and send the target candidate to the cleverly-prepared site of his (or her?) execution. As long as he is successful, no-one will ever know about the deception--even necromancy will only implicate the one impersonated...